code: def test_call_cudnn_backward(self):
      with chainer.using_config("use_cudnn", self.use_cudnn):
          y = self.forward()
          y.grad = self.gy
          default_func = cuda.cupy.cudnn.activation_backward
          with testing.patch("cupy.cudnn.activation_backward") as func:
              func.side_effect = default_func
              y.backward()
              self.assertEqual(func.called, self.expect)
  
file_path: chainer/tests/chainer_tests/functions_tests/activation_tests/test_relu.py
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 4 for calling the TestReLUCudnnCall obj's underlying member method code with example usage: obj.test_call_cudnn_backward() without return types